The invention relates to a sheet-braking system for a delivery of a sheet-process machine, in particular, a printing machine, having a braking belt which revolves during operation and undergoes periodic decelerating and accelerating phases, the braking belt including a braking strand passable over a suction region providing a suction action passing through the braking strand, and further relates to a rotary printing machine equipped with the sheet-braking system.
A sheet-braking system of the aforementioned type has become known heretofore, for example, from German Patent 196 49 824. A suction conveyor disclosed in this document is used, in accordance with an exemplary embodiment described therein, as a sheet-braking system. The latter includes a braking belt which revolves non-uniformly during operation and has a braking strand, a respectively processed sheet being transferable to the braking belt at the processing speed of the sheet, without any speed relative to the braking belt, by a sheet-transporting sheet conveyor, and being pressable a sheet-transporting sheet conveyor, and being pressable against the braking strand with a suction effect, so that a sheet respectively pressed against the braking strand follows the speed variation of the braking belt under a retaining force acting between the sheet and the braking strand, and is thus braked when the braking belt is decelerated.
For the purpose of producing the suction action, a suction-chamber device is provided which is connected to a negative-pressure generator via a suction-intake union, and subjects a suction-air flow passing through the suction-chamber device to a throttling action, and extends in the form of a channel in the travel direction of the braking strand. In a configuration of the conventional suction conveyor which is suitable, in particular, for braking sheets, the suction intake union or opening is provided at a downline end of the channel, as viewed in the travel direction of the braking strand. This measure is taken in conjunction with the throttling action so that, during the progressive release of the suction-chamber device by the sheet guided by the braking strand, a retaining force would still be maintained between the sheet and the braking strand, this retaining force being necessary whenever the sheet is to be braked by the braking strand. However, this retaining force decreases with the progressive release of the suction-chamber device, so that, in comparison with the case wherein the suction-chamber device is entirely covered by a sheet, lower retaining forces, and thus lower deceleration of the respective sheet, can be achieved. With relatively high processing speeds, however, this requires relatively long decelerating distances for braking the sheets to an adequate depositing speed, which must be selected so that the braked sheets released by the sheet-braking system come into contact with leading-edge stops, and are aligned thereon for a straight-edge construction of a pile or stack formed from the sheets, without damaging any of the leading edges of the sheets, respectively.
The relatively long decelerating phases which are consequently necessary for the non-uniformly revolving braking belt result, particularly during the processing of sheets of a maximum format that can be transported by the sheet conveyor, in a sheet which is transported over the sheet-braking system at the processing speed by the sheet conveyor, with positive guidance at the leading edge thereof, having a leading section already located in the region of the sheet-braking system while a trailing section of an advanced or preceding sheet that is still being braked adheres to the braking strand. This may result, however, in mutual contact between successive sheets in the case wherein relative speeds exist between the sheets, and in consequent damage to the printed images applied to the sheets.
It is accordingly an object of the invention to provide a sheet-braking system for a delivery of a sheet-processing machine, in particular, a printing machine, wherein sheets passing through the machine are braked from a processing speed to a depositing speed over the shortest possible distance.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a sheet-braking system for a delivery of a sheet-processing machine, comprising a braking belt revolving during operation and undergoing periodic decelerating and accelerating phases, said braking belt including a braking strand passable over a suction region providing a suction effect passing through said braking strand, said suction region being overlapped throughout the duration of a respective decelerating phase, by a respective sheet deposited on the braking strand.
In accordance with another feature of the invention, a respective decelerating phase is terminatable with the arrival of the trailing edge of a respective sheet at the suction region.
In accordance with a further feature of the invention, the suction region is limited to a downline section of the braking strand, as viewed in the travel direction of the braking strand.
In accordance with an added feature of the invention, the sheet-braking system includes a beginning of a respective decelerating phase of the braking belt after the trailing edge of a respective sheet deposited on the braking strand has reached the braking strand.
In accordance with another aspect of the invention, there is provided a sheet-processing rotary printing machine, including a sheet-braking system for a delivery of the sheet-processing machine, comprising a braking belt revolving during operation and undergoing periodic decelerating and accelerating phases, the braking belt including a braking strand passable over a suction region providing a suction effect passing through the braking strand, the suction region being overlapped throughout the duration of a respective decelerating phase, by a respective sheet deposited on the braking strand.
In accordance with a further aspect of the invention, there is provided a method of operating a sheet-braking system for a delivery of a sheet-processing machine, which comprises, during operation, revolving a braking belt with periodic decelerating and accelerating phases, passing the braking belt, including a braking strand thereof, over a suction region providing a suction effect passing through the braking strand, overlapping the suction region throughout the duration of a respective decelerating phase, by a respective sheet deposited on the braking strand.
In accordance with an added mode, the method of the invention includes terminating a respective decelerating phase upon the arrival of the trailing edge of a respective sheet at the suction region.
In accordance with a concomitant mode, the method of the invention includes beginning a respective decelerating phase of the braking belt after the trailing edge of a respective sheet deposited on the braking strand has reached the braking strand.
Thus, in order to achieve the object of the invention, a sheet-braking system of the type mentioned in the introduction hereto is provided so that, throughout the duration of a respective decelerating phase, the suction region of the sheet-braking system is overlapped by a respective sheet which is deposited on the braking strand.
This measure prevents the situation wherein the retaining force which presses a respective sheet against the braking strand decreases during a respective decelerating phase.
Throughout the duration of a respective decelerating phase, a constant retaining force is thus available and, with a corresponding magnitude of the retaining force, the latter allows a greater deceleration of a respective sheet than a retaining force which decreases during a deceleration.
In a preferred configuration, the overlapping of the suction region for the duration of a respective decelerating phase is realized in that a respective decelerating phase is terminated at the latest with the arrival of the trailing edge of a respective sheet at the suction region.
Furthermore, the suction region is preferably restricted or limited to a downline section of the braking strand, as viewed in the travel direction of the braking strand.
In a further preferred configuration, a respective decelerating phase begins once the trailing edge of a respective sheet deposited on the braking strand has reached the braking strand.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a sheet-braking system for a delivery of a sheet-processing machine and method of operation, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: